Extraction of fibrous cellulosic material with ammonia following treatment with chlorine,chlorine dioxide or other reagents



EP'IU I FIPBSOS 3,472,731 EXTRACTION F FIBROUS CELLULOSIC MATE- RIAL WITH AMMONIA FOLLOWING TREAT- MENT WITH CHLORINE, CHLORINE DIOXIDE OR OTHER REAGENTS Norman Liebergott, Chomedy, Quebec, and Frederic H. Yorston, Montreal, Quebec, Canada, assignors to Pulp and Paper Research Institute of Canada, Pointe-Claire, Quebec, Canada No Drawing. Filed Sept. 8, 1966, Ser. No. 577,813 Claims priority, application Canada, Oct. 12, 1965, 942,675 Int. Cl. D21c 3/02, N08

US. Cl. 162-63 8 Claims ABSTRACT OF THE DISCLOSURE In the multi-stage bleaching of a chemical cellulosic pulp a process for the extraction of alkali-soluble ligneous impurities from the pre-treated pulp which process comprises adjusting the moisture content of the pulp to a level of from 40 to 85%, shredding or fiuffing the pulp into fiber and fiber aggregates and then adding ammonia, preferably diluted with a non-reactive gas which is nitrogen, steam or air to the shredded or flufied pulp mass at a temperature of at least 60 C. The contact time between the ammonia gas and the pulp is usually of the order of about 1 to 30 minutes and the temperature is desirably from 60 to 100 C. Desirably, the shredded or fluffed pulp is pre-heated to a temperature from 60 to 100 C. prior to exposure to the gaseous ammonia.

This invention relates to the alkaline extraction of pretreated pulp. By pre-treated pulp is meant pulp which has been pre-treated to render the ligneous encrustants soluble in dilute alkali. Non-limiting examples of treating agents include chlorine, chlorine dioxide and oxides of nitrogen.

Chlorination of unbleached pulp so changes ligneous impurties that they become, in part, soluble in water, while of the proportion not readily soluble in water, a part is soluble in alkaline solutions such as dilute solutions of sodium hydroxide, sodium sulphite or ammonia. After pulp has been chlorinated and washed with water, it is advantageous and indeed customary to treat the pulp with a warm or hot solution of alkali, 'for example, sodium hydroxide to effect removal of impurities insolu- 'ble in water alone. In multi-stage bleaching of paper pulps, treatment with sodium hydroxide is generally conducted at 10 to 14 percent consistency, at 40 to 60 C., with retention times of 60 to 120 minutes. The quantity of sodium hydroxide used amounts to l to percent of the weight of pulp. Sodium hydroxide solution will also dissolve ligneous impurities in unbleached pulp which has been pretreated with chlorine dioxide or with dinitrogen tetroxide or with nitrous acid.

It has been suggested to use ammonia as an alkaline extraction agent in the place of sodium hydroxide. It has been supposed also that sodium hydroxide could be replaced, advantageously, by a smaller proportion by weight of ammonia because the molecular weight of ammonia is 17, but the molecular weight of sodium hydroxide is 40 or more than twice as great. It has been found, however, by experiment that ammonia is less eflicient than a chemically equivalent quantity of sodium hydroxide in extracting chlorinated pulps at consistency at 60 C. Further, F. Hedborg discloses in Svensk Papperstidning, volume 46, page 390, that ammonia is less elfective than an equivalent quantity of sodium hydroxide in extraction of pre-chlorinated kraft Wm sauna Pam! all we \I w n! 3,472,731 Patented (Jota 14, 1969 pulps at 10% consistency and at temperatures of 15 C. and C.

An object of one aspect of the present invention is the provision of an improved process for the alkaline extraction of pretreated, e.g. pro-chlorinated pulp.

An object of another aspect of the present invention is the provision of an improved accelerated ammonia extraction procedure for the extraction of pre-treated, e.g pre-chlorinated pulp.

By a broad aspect of the present invention, there is provided, in the ammonia extraction of pre-treated, e.g. pre-chlorinated pulp, the improvement of exposing fluflfed pre-treated, e.g. pre-chlorinated pulp at .a moisture con= tent of about 4085% to an atmosphere comprising gas eous ammonia, either alone or in admixture with other gases, at a temperature of about 60-100 C. for a retention time of about l30 minutes.

By another aspect of the present invention, there is provided a process for the alkaline extraction of pretreated, e.g. pre-chlorinated pulp, which comprises: finely dividing said pre-treated, e.g. pre-chlorinated pulp into fiber aggregates at a moisture content of about 40-85 preheating said fiber aggregates to a temperature of about 60l00 C.; exposing said preheated fiber aggregates to an atmosphere comprising gaseous ammonia, either alone or in admixture with other gases, for a retention time of about 1 to about 30 minutes; and maintaining the temperature during said retention time to within the range of 60-100 C.

It has been found according to an important aspect of the present invention, the retention time is substantially reduced and heat is saved because less water is heated to the reaction temperature. It has also been found that there is an unexpected saving of ammonia. It has been found that there is no need to supply a large quantity of ammonia. Furnishing a dosage of ammonia, one half or less by weight, of the quantity of NaOH supplied on the dry weight of fiber is sufiicient to reduce the Kappa number of pre-chlorinated pulps to similar values.

The resulting treated, e.g.. chlorinated anci ammonia extracted pulp maybe oxidized to high brightness without significant loss of cellulose viscosity.

In the operation of a preferred aspect of this invention the moisture content of the chlorinated pulp is adjusted to the desired level, between 40 and 85 percent of the weight of wet pulp, by adding water to the pulp if it is initially too dry, or by thickening and pressing if the initial water content is greater than 85 percent. Pulp at the desired consistency is comminuted into a dispersion of fiber aggregates, for example, by shredding or passage through a disk mill or refiner having a wide separation between the plates. The moist, shredded or fluffed pulp is preheated by warm moist air or steam, or a warm moist inert gas, to a temperature between 60 and C. and is then exposed to the gaseous ammonia extracting agent, for a period of one to 30 minutes. The gaseous ammonia extracting agent may be undiluted=ammonia gas, or ammonia diluted with air, or steam, or nitrogen or any other inert gas. The treated pulp is then dropped into water and washed.

The following are examples of this invention.

Example I An unbleached kraft pulp from coniferous wood characterized by a Roe chlorine number 3.99 Kappa num ber 23.8 and 0.5 percent cupri-ethylenediamine viscosity of 27 cp. after acid chlorite treatment, was treated with gaseous chlorine at 30 C. for one minute; the pulp was then washed, pressed to 20 percent consistency and shredded. One portion of the treated pulp was placed in a tower, tower and contents preheated to 99 C. by direct steaming. An ammonia-steam mixture, containing 1 percent ammonia n the weight of dry fiber, was passed upward through the pulp for a contact period of 1 minute. Unreacted. ammonia passed from the tower through a condenser, was absorbed in dilute hydrochloric acid and determined. Consumption of ammonia was 0.92 percent of the weight of dry fiber. The pulp was then washed. Characteristics of the extracted pulp were: Kappa number 7.5, CED viscosity 26 cp.

A second portion of the same chlorinated-washed pulp was treated with 2 percent of its weight of sodium hydroxide at 10 percent consistency for 60 minutes at 60 C. Characteristics of the soda extracted pulp were Kappa number 7.5, CED viscosity 27 cp.

Example II An unbleached kraft pulp from coniferous wood characterized by a Roe chlorine number 13.2, Kappa number 68.0 and 0.5 CED viscosity 55.6, after acid chlorite treatment was treated with. gaseous chlorine at 30 C. for one minute. The pulp was then washed, pressed to 20 percent consistency and shredded.

One portion of the treated pulp was placed in a tower, tower and contents preheated to 99 C. by direct steaming. An ammonia-steam mixture, containing 2 percent ammonia on the weight of dry fiber, was passed upward through the pulp for a contact period of one minute, Unreacted ammonia passed from the tower through a condenser, was absorbed in dilute HCl acid and determined. Consumption of ammonia was 1.97 percent of the weight of pulp. The sample was then washed. Characteristics of the extracted pulp were: Kappa number 15.6, CED viscosity 51 cp.

A second portion of the same chlorinated, washed pulp was treated with 5 percent of its weight of sodium hy droxide at percent consistency for 60 minutes at 60 C.

Characteristics of the soda-extracted pulp were: Kappa number 15.8, CED viscosity 52 cp.

The responses 01": the ammonia-extracted and sodaextracted pulps to oxidation with chlorine dioxide were similar. The pulp of Example I was brightened to 80% Elrepho brightness and the pulp of Example II to 70% Elrepho brightness.

The ammonia extracted pulp of Example I was bleached to 90 percent brightness with a second additional treatment of chlorine dioxide, with no significant loss of cellulose viscosity.

Example III An unbleached kraft pulp from coniferous wood characterized by a Roe chlorine number 3.97, Kap a number 23.5, was treated with gaseous chlorine dioxide in accordance with the procedure preferably consisting of adjusting the moisture content of the fibers to a level of from 60% to 70%, adding chlorine dioxide gas diluted with an inert gaseous solvent such as air, steam, nitrogen or an inert gas where the partial pressure of chlorine dioxide is 100 millimetres of mercury or less, and exposing the fiber aggregate to the diluted chlorine dioxide gas for a period of from 5 to 30 minutes at temperature of from 65 to 100 C. The pH range of the mixture may be controlled by using, if necessary, a mild alkali so that the final pH is within the range of from 3.5 to 6.5, The aforesaid procedure is disclosed and claimed in pending Canadian application Ser. No. 908,947, filed .Aug. 7, 1964 (corresponding to US. application Ser. No. 407,908 filed Oct. 30, 1964), now abandoned. The

4 pulp was then washed, pressed to 20 percent consistency and shredded.

One portion of the treated pulp was placed in a tower, tower and contents pre-heated to 99 C. by direct steaming. An ammonia-steam mixture, containing 0.68 percent ammonia on the weight of dry fiber, was passed upward through the pulp for a contact period of 1 minute. The pulp was then washed. Kappa number of the extracted pulp was 5.7.

A second portion of the same chlorine dioxide treated and. washed pulp was further treated with 1.5 percent of its weight of sodium hydroxide at 10 percent consistency for 60 minutes at 60 C. Kappa number of the soda extracted pulp was 5.4.

The responses of the ammonia-extracted and sodaextracted pulps to oxidation with chlorine dioxide were similar. Both pulps were brightened to percent Elrepho brightness.

We claim:

1. In the multi-stage bleaching of a chemical cellulosic pulp which includes bleaching said pulp to render ligneous impurities contained therein soluble in dilute alkali and extracting said alkali-soluble ligneous impurities from said pulp, the improvement which comprises extracting said impurities from the bleached pulp at a moisture con tent of about 40 to in fluflfed or shredded form as fibers or fiber aggregates and at a temperature from about 60 C. to 150 C. with gaseous ammonia for a time and in an amount sufiicient to extract said alkalisoluble ligneous impurities from said pulp.

2. A process as claimed in claim 1 in which the ligneous imprities in said pulp are rendered alkali-soluble by treat ment with a reagent selected from the group consisting of chlorine, chlorine dioxide and mixtures thereof.

3. Av process as claimed in claim 1 in which the ligneous impurities in said pulp are rendered alkalisoluble by treatment with oxides of nitrogen.

4. A process as claimed in claim 1 in which the temperature is from about 60 to 100 C.

5. A process as claimed in. claim 1 in which the Con-- tact time between the gaseous ammonia and the pulp is from 1 to 30 minutes.

6. A process as calimed in claim 1 in which the pulp is a wood pulp.

7 A process as claimed in claim 1 in which the gaseous ammonia is in admixture with a non-reactive gas.

8. A process as claimed in claim 1 in which the fluti'ed or shredded pulp is heated to a temperature in the range 60 to 100 C. prior to exposure to the gaseous ammonia.

References Cited UNITED STATES PATENTS 1,345,776 7/1920 Hofste 16289 2,964,518 12/1960 Snyder l6263 X FOREIGN PATENTS 175,330 2/1922 Great Britain. 321,282 11/1929 Great Britain. 601,643 5/1948 Great Britain.

S. LEON BASHORE, Primary Examiner R. D. BASEESKY', Assistant Examiner US. Cl. X.R. 

